A Vz. 58 or an SKS in 5.45x39 would be an interesting gun indeed, considering 5.45x39 7N6 is extremely ballistically superior to the standard 7.62x39 round. I've fired plenty of 5.45 AK's in the US and I can tell you that they're both softer shooting and more accurate than a 7.62x39 AK or SKS.
There is SO MUCH of this ammo and it's still being churned out today in multiple places around the world. I think we're missing an opportunity by not having a nice tactical rifle in this caliber.